linux-kernel - [PATCH 4.9 08/16] ip_gre: add validation for csum

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Date:   Wed,  1 Sep 2021 14:26:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+ff8e1b9f2f36481e2efc@...kaller.appspotmail.com,
        Shreyansh Chouhan <chouhan.shreyansh630@...il.com>,
        Willem de Bruijn <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 08/16] ip_gre: add validation for csum_start

From: Shreyansh Chouhan <chouhan.shreyansh630@...il.com>

[ Upstream commit 1d011c4803c72f3907eccfc1ec63caefb852fcbf ]

Validate csum_start in gre_handle_offloads before we call _gre_xmit so
that we do not crash later when the csum_start value is used in the
lco_csum function call.

This patch deals with ipv4 code.

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Reported-by: syzbot+ff8e1b9f2f36481e2efc@...kaller.appspotmail.com
Signed-off-by: Shreyansh Chouhan <chouhan.shreyansh630@...il.com>
Reviewed-by: Willem de Bruijn <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 net/ipv4/ip_gre.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 9609ad71dd26..fe1801d9f059 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -353,6 +353,8 @@ static void __gre_xmit(struct sk_buff *skb, struct net_device *dev,
 
 static int gre_handle_offloads(struct sk_buff *skb, bool csum)
 {
+	if (csum && skb_checksum_start(skb) < skb->data)
+		return -EINVAL;
 	return iptunnel_handle_offloads(skb, csum ? SKB_GSO_GRE_CSUM : SKB_GSO_GRE);
 }
 
-- 
2.30.2